1. Field of the Invention
The present invention relates to a memory module and, more particularly, to a memory module having memory chips on both sides thereof and a signal line arrangement method thereof.
2. Description of the Related Art
A memory module generally includes a printed circuit board (PCB) and memory chips. The memory chips mounted on the PCB can be arranged on both sides of the PCB in a mirrored configuration. That is, a same signal applying ball (pin) of each memory chip mounted on both sides of the PCB can be arranged on both sides of the PCB in a mirror form.
A conventional signal line arrangement method includes forming a via passing through a central location of pads in contact with the same signal applying balls (pins) of memory chips on both sides of the PCB in a mirrored configuration, and connecting a signal line to a same signal applying ball of one side from the via and connecting a signal line to the same signal applying ball of the other side from the via.
However, this method has a spatial limitation to arranging signal lines arranged around the via since the via has to be located at a center of the pads to which the same signal applying balls (pins) arranged on both sides of the PCB in a mirror form contact. Further, since a time for a signal to pass through the via is not considered, signal transmission times spent for a signal to be transmitted to the pads which the same signal applying balls (pins) arranged on both sides in a mirror form contact can differ, and thus if a signal which operates at a high frequency is transmitted, signal distortion can occur.
Another conventional signal line arrangement method of the memory module is to arrange the via at a location close to one of the pads which the same signal applying balls (pins) contact according to the arrangement of signal lines arranged around the via without forming the via on the central location of the pads which the same signal applying balls (pins) arranged in the mirror form contact. Here, signal lines arranged on both sides are same in length of from the via to the same signal applying balls (pins). That is, in order to make equal a length of the signal line from the via to the pad which is arranged on one side of the PCB and the same signal applying balls (pins) contact and a length of the signal line from the via to the pad which is arranged on the other side of the PCB and the same signal applying balls (pins) contact, one signal line is arranged in a straight line from, and the other signal line is arranged in a bent form.
Thus, this method has an advantage in that signals can be transmitted at the same time point since the signal lines are the same in length from the via to the same signal applying balls arranged on both sides of the PCB and is also efficient in arranging the signal lines around the via. However, a length of the signal line from via to the pad can become lengthy because the via is arranged at a location close to one of the pads which the same signal applying balls (pins) contact. Thus, this method has a limitation in that it is not conductive to transmit a high-frequency signal, like the first method for arranging the via at the central location of the same signal applying balls (pins) described above. Similar to the first method, since a time to pass through the via is not considered, signal distortion can occur when the high-frequency signal is transmitted, because signal transmission times for a signal to be transmitted to the pads in contact with the same signal applying balls (pins) arranged on both sides of the PCB in a mirrored configuration can differ.